1) Field of the Invention
The attention of car manufacturers is currently oriented towards reducing the damage that a vehicle undergoes as a result of collisions at relatively low speeds, typically lower than 15-16 Km/h. The protective structure according to the present invention is preferably suitable for impacts having the above characteristics.
The devices used on vehicles for limiting damage during said collisions on the rear side, consist of completely metallic, generally steel, crosspieces, positioned between the vehicle chassis and bumpers; the crosspiece normally rests and is directly fixed to the side-rails, or absorption devices of the metallic type (crash boxes), to which the crosspiece is connected, are fixed to the side-rails. These absorption elements are also known as “sacrificial elements”, which, in the case of collision, absorb most of the impact energy by deforming, and at the same time, preventing the deformation of the vehicle chassis.
A protective structure for vehicles of the known type, typically comprises a pair of impact absorption elements, situated in correspondence with the lateral side-rails of the vehicle chassis, on which a crosspiece is assembled over which a bumper strip is superimposed.
The crosspiece is normally made of a metallic material, for example aluminum or steel or plastic, whereas the sacrificial elements can be made of a metallic material or plastic material or a complex of elements made of different materials (honeycomb structures).
The sacrificial elements form the only connection elements between the protective structure of the vehicle with the vehicle chassis itself.
During collision, an impactor will first strike the crosspiece which transfers the load onto the sacrificial elements (in a percentage proportional approximately similar to the impact distance with respect to the two elements).
These structures, for post centered impacts at an equal distance between two sacrificial elements, require extremely rigid crosspieces to be able to transfer the maximum possible force onto the sacrificial elements; this force is defined by the collapse value of the crosspiece. This force, moreover, will then be transferred equally on each side.
If the crosspiece were extremely rigid (which, by nature, is impossible) it would tend to transfer the force without collapsing and consequently deform the two sacrificial elements thus giving a force to the impactor equal to the sum of the collapse forces of the sacrificial elements.
If the force transmitted to each crash box or sacrificial element were light, it would be the crosspiece that would be deformed under the impact.
In order to improve the technical solution, or reduce the intrusion of the obstacle, it is necessary to increase the weight of the crosspiece and consequently of the vehicle.
The Applicant has considered the problem of increasing the resistance of said protective structure without having to reinforce the crosspiece of the structure and therefore without increasing the weight of the vehicle.